WO2013152297A1

WO2013152297A1 - A wind turbine with a ring airfoil shroud having a flap

Info

Publication number: WO2013152297A1
Application number: PCT/US2013/035464
Authority: WO
Inventors: Walter M. Presz, Jr.; Michael J. Werle; Robert H. Dold; Ercan Dumlupinar
Original assignee: Flodesign Wind Turbine Corp.
Priority date: 2012-04-05
Filing date: 2013-04-05
Publication date: 2013-10-10
Also published as: CN104334872A; CA2869608A1; EP2834516A1; US20130266438A1

Abstract

A ring airfoil with a voluminous leading edge region, an intermediate region, a trailing edge region including a flap. The ringed structural leading edge region combined with a rigid trailing edge region having intermediate discrete support portions extending therebetween provides sufficient rigidity to support the flap on the trailing edge region while using a membrane intermediate surface to form a portion of the intermediate region of the airfoil.

Description

A WIND TURBINE WITH A RING AIRFOIL SHROUD HAVING A FLAP

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application Serial No. 61/620,792, filed on April 5, 2012 and U.S. Provisional Application Serial No. 61/763,805 filed on February 12, 2013, respectively, the disclosures of which are incorporated herein by reference in their entirety.

BACKGROUND

[0002] The present disclosure relates to the field of ring airfoils and more particularly to shrouded turbines comprising unique airfoil characteristics. More specifically, taught herein are embodiments directed to a modified ringed airfoil that provides a reduced cross sectional area for reduced side loads and reduced material use while maintaining performance. Airfoils with structural leading edges engaged with substantially curved planar surfaces are common in the fields of light aircraft and sailing vessels. Curved planar surfaces are defined as those that have an upper surface that is substantially parallel to a lower surface. Such an airfoil has a reduced cross sectional area from that of an airfoil with continuous varying distance between the upper and lower surface. Utility scale wind turbines used for power generation have one to five open blades comprising a rotor. Rotors transform wind energy into a rotational torque that drives at least one generator that is rotationally coupled to the rotor either directly or through a transmission to convert mechanical energy to electrical energy.

[0003] A shrouded wind turbine has been described in U.S. Patent Application Serial No. 12/054,050, the disclosure of which is incorporated herein by reference in its entirety.

SUMMARY

[0004] The embodiments taught herein relate to a ringed airfoil with a cross section that includes a leading edge portion with varying distance between the upper and lower surface, a symmetrical region having symmetry about the chord line through said symmetrical region wherein in one embodiment the upper surface is substantially parallel to a lower surface, and a trailing edge region providing a flap on the trailing edge that is substantially perpendicular to the chord line of the airfoil. Providing a flap on the trailing edge of such an airfoil further reduces the cross sectional area of the airfoil compared to convention air foils.

[0005] Lack of support structure(s) in an intermediate symmetrical region does not allow for a flap to function when configured perpendicular to the chord line of the resulting airfoil. Such a flap on the trailing edge of a curved planar surface would flex until the flap failed to have any effect on the flow over the airfoil. In embodiments, taught herein, an orientation of the flap can be fixedly with respect to the chord line of the ring airfoil. For example, in one embodiment, the ring airfoil can include a rigid trailing edge that provides sufficient structure for a flap that is disposed substantially perpendicular to the chord of the airfoil.

[0006] In one embodiment, an aerodynamically contoured ring airfoil is disclosed. A body extends circumferentially about a center axis having an aerodynamic structure formed by an outer surface and an inner surface. The outer and inner surfaces extend axially with respect to the center axis along a camber line. The body includes a leading edge region, a trailing edge region, and an intermediate region extending between the leading edge region and the trailing edge region. The leading edge region having a non-uniform cross-sectional thickness extending along the camber line defined by the outer surface and the inner surface of the body. The trailing edge region includes a flap extending therefrom and orientated at an angle with respect to a chord line of the body to allow a fluid flow flowing along the inner surface to remain attached to the inner surface.

[0007] In one example, embodiment, an energy extracting shrouded fluid turbine is disclosed that includes an energy extracting assembly and an airfoil. The energy extracting assembly includes a rotor disposed radially about a center axis. The airfoil has a body extending circumferentially about the center axis. The body has an aerodynamic structure formed by an outer surface and an inner surface. The outer and inner surfaces extend axially with respect to the center axis along a camber line. The body includes a leading edge region a trailing edge region, and an intermediate region that extends between the leading edge region and the trailing edge region. The leading edge region has a non-uniform cross-sectional thickness extending along the camber line defined by the outer surface and the inner surface of the body. The trailing edge region includes a flap extending therefrom and orientated at an angle with respect to a chord line of the body to allow a fluid flow flowing along the inner surface to remain attached to the inner surface.

[0008] In some embodiments, the flap extends from the trailing edge region perpendicularly to the chord line, has a length of about one-tenth to about one-third a length of the chord line, and/or includes at least one perforation to permit fluid flow through the flap.

[0009] In some embodiments, the flap extends from a trailing edge of the airfoil.

[0010] In some embodiments, the flap extends between a first ring structure and a second ring structure, the first and second ring structures providing a hoop strength to the flap.

[0011] In some embodiments, the first ring structure provides a hoop strength to the trailing edge region of the body.

[0012] In some embodiments, the intermediate region includes at least one intermediate support portion extending between the leading edge region and the trailing edge region. In some embodiments, the intermediate support portion is composed of a rigid material and/or has a uniform cross-sectional thickness extending along the mean camber line defined by the outer surface and the inner surface of the body.

[0013] In some embodiments, the intermediate region includes at least one intermediate membrane portion extending between the leading edge region and the trailing edge region. In some embodiments, the intermediate membrane portion has a uniform cross-sectional thickness extending along the mean camber line defined by the outer surface and the inner surface of the body and/or is composed of a non-rigid material.

[0014] In some embodiments, the intermediate support portions provide structural support to the intermediate membrane portion.

[0015] Any combination or permutation of embodiments is envisioned. Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the present disclosure. BRIEF DESCRIPTION

[0016] The present disclosure relates to a ringed airfoil having a unique airfoil cross sectional shape with rigid portions at the leading and trailing edges, providing hoop strength that supports a membrane intermediate portion and allows for a trailing edge flap. In example embodiments, a combination rigid structural portions and non- rigid membrane portions can be used to form an example ring airfoil that provides for controlling a boundary layer at the trailing edge of the airfoil and provides for increased suction through the center of the ring airfoil compared to conventional ring airfoils. Such an airfoil provides a means of utilizing lightweight materials while generating aerodynamic circulation resulting in a pressure differential on the inside of the ring airfoil as compared to the exterior of the airfoil.

[0017] In one embodiment, the ring airfoil surrounds a rotor and electrical generation equipment of a shrouded fluid turbine. The fluid turbine may have a single shroud, or may include multiple shrouds. The shrouds are comprised of generally ring airfoils that may include a turbine shroud and an ejector shroud.

[0018] In one embodiment, the turbine shroud houses a rotor and includes mixing elements at the trailing edge of the ring airfoil that are in fluid communication with an ejector shroud fluid stream providing a mixer-ejector pump. The shroud(s) generate aerodynamic circulation resulting in suction on the inside of the turbine shroud and are part of a tightly coupled system that, combined with the mixer-ejector pump, allow the acceleration of more air through the turbine rotor than that of un-shrouded designs, thus increasing the amount of power that may be extracted by the rotor.

[0019] In the field of fluid dynamics, the term "stall" refers to the condition in which fluid flow separation occurs. In other words, the fluid flowing closely around the airfoil starts to detach from the surface and become turbulent. The embodiments taught herein are described be described in view of a mixer only embodiment and a mixer-ejector turbine embodiment. One skilled in the art will recognize that the example embodiments of the present disclosure may be readily applied to any ringed airfoil including any number of ducted or shrouded fluid turbine applications. The recitation of a mixer only embodiment and a mixer-ejector turbine embodiment is therefore not intended to be limiting in scope as is solely for convenience in illustrating an example embodiment of the present disclosure. Separation of airflow from the aerodynamic surfaces through a mixer turbine and/or Mixer-Ejector Turbine (MET) can be substantially prevented to advantageously maintain an efficiency of the turbine and to advantageously mitigate diffuser stall.

[0020] The Kutta-Joukowski theorem describes the circulation around any closed surface. It is this circulation that causes lift and increases the air flow through the shrouded turbine. The theorem determines the lift generated by one unit of span in a closed body and states that when the circulation so is known, the lift L per unit span (or L^: ) of a cylinder can be calculated using the following equation:

Equation 1 where !¼? and

are the fluid density and the fluid velocity far upstream of the cylinder, respectively. The circulation * ; ; is defined as a line integral in the following equation:

Γ_∞ = Φ V cos Θ ds Equation 2

[0021] Improved circulation through the use of an aerodynamic modified region (AMR) on the trailing edge of the mixer and/or ejector shroud airfoil provides for increased performance of the shrouded turbine. The Kutta condition (as a function of the Kutta-Joukowski theorem) controls circulation generated by the airfoil and generally prevents flow separation from the aerodynamic surfaces until the flow reaches the trailing edge.

[0022] Fluid moves through or across an airfoil shape and produces an aerodynamic force. The component of the aerodynamic force that is perpendicular to the direction of fluid flow is called lift and the component parallel to the direction of fluid flow is called drag. Additionally, an airfoil has a suction surface and a pressure surface through which lift forces are generated. The airfoil suction side is defined by the airfoil surface turning away from the oncoming flow. Usually the top (or outer) and bottom (or inner) airfoil surface are joined by a curved leading edge and a sharp trailing edge. The camber line of the airfoil dissects this trailing edge at one end and extends to the apex, or most upwind point, of the leading edge. Aerodynamic circulation is a result of flow turning and is usually limited by flow separation on the airfoil suction side.

[0023] An example embodiment of the present disclosure provides for obtaining increased airfoil circulation, or effective flow turning, as compared to conventional airfoil structures by modifying the airflow across the pressure side of the airfoil aerodynamic surfaces, especially proximate to the trailing edge. In example embodiments of the present disclosure, an increase in circulation can be accomplished by increasing surface turning on the pressure side of the airfoil. Increasing the turning on the pressure side is possible because the surface is turning into the flow direction and the flow is less apt to separate from the surface on the pressure side. In one embodiment, increasing the flow turning can be achieved using a trailing edge flap on the top (or outer) surface of the airfoil (i.e., the pressure side).

[0024] In example embodiments, the flap can be a flat plate or other protrusion from the trailing edge. In some embodiments, a length of the trailing edge flap can be on the order of 1— 30% of a length of the airfoil chord extending between the leading edge and the trailing edge of the airfoil. The trailing edge flap can be oriented perpendicular to the chord line and disposed on the airfoil pressure side at or proximate to the trailing edge. In some embodiments the trailing edge flap is perforated. The perforations can allow the flap to provide an effective height to cause increased circulation while also providing reduced drag.

[0025] The use of a flap effectively changes the flow-field in the region of the trailing edge of the ring airfoil by introducing contra-rotating vortices aft of the flap, which alters the Kutta condition and circulation in the region.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a front, perspective view of an example ring airfoil of the present disclosure.

Figure 2 is a side, cross sectional view of the example airfoil of Figure 1. Figure 3 is a side, cross sectional view of the example airfoil of Figure 1. Figure 4 is a side, detail, cross sectional view of the example airfoil of the embodiment of Figure 1.

Figure 5 is a side, cross sectional view of the example airfoil of the embodiment of Figure 1 with flow lines.

Figure 6 is a front, perspective view of another example ring airfoil of the present disclosure.

Figure 7 is a side, cross sectional view of the example airfoil of Figure 6.

Figure 8 is a front, right, perspective view of an example shrouded turbine for which the turbine shroud corresponds to the example airfoil of Figure 1.

Figure 9 is a front, right, perspective view of an example shrouded turbine for which the turbine shroud corresponds to the example airfoil of Figure 6.

.Figure 10 is a front, right, perspective view of an example mixer-ejector turbine incorporating the example airfoils of Figures 1 and 6.

Figure 11 is a rear, right, perspective view of an example mixer-ejector turbine of Figure 10.

Figure 12 is a side, perspective, detail cross section of an example mixer-ejector turbine of Figure 10 and Figure 11, cut through the outward turning mixer airfoil section.

Figure 13 is a side, perspective, detail cross section of the mixer-ejector turbine of Figure 10 and Figure 11, cut through the inward turning mixer airfoil section.

Figure 14 is a detailed view of the flaps disposed on a trailing edge regions of the example mixer ejector turbine of Figure 10 and Figure 11.

Figure 15 is a front, right, perspective view of another example mixer-ejector turbine for which the turbine shroud and the ejector shroud have a faceted configuration. Figure 16 is a side, perspective, detail cross section of an example mixer-ejector turbine of Figure 15, cut through the outward turning mixer airfoil section.

Figure 17 is a front, right, perspective view of another example shrouded turbine for which the turbine shroud has a faceted configuration.

DETAILED DESCRIPTION

[0026] A more complete understanding of the components, processes, and apparatuses disclosed herein can be obtained by reference to the accompanying figures. These figures are intended to demonstrate the present disclosure and are not intended to show relative sizes and dimensions or to limit the scope of the example embodiments.

[0027] Although specific terms are used in the following description, these terms are intended to refer only to particular structures in the drawings and are not intended to limit the scope of the present disclosure. It is to be understood that like numeric designations refer to components of like function.

[0028] The term "about" when used with a quantity includes the stated value and also has the meaning dictated by the context. For example, it includes at least the degree of error associated with the measurement of the particular quantity. When used in the context of a range, the term "about" should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the range "from about 2 to about 4" also discloses the range "from 2 to 4."

[0029] A shrouded turbine can include a turbine shroud with or without mixing lobes on a trailing end of the turbine shroud. As set forth previously, a shrouded turbine that includes a mixer shroud is one suitable example of a ringed airfoil in which the example embodiments of the present disclosure may be utilized. The turbine shroud includes a cambered shroud, wherein the shroud is a substantially ringed airfoil. The turbine shroud contains a rotor, which extracts power from a primary fluid stream. The turbine shroud provides for increased flow through the rotor allowing increased energy extraction due to higher flow rates compared to shroudless fluid turbines.

[0030] A Mixer-Ejector Turbine (MET) can provide an improved means of generating power from fluid currents using a mixer/ejector pump. As set forth previously, a MET is one suitable example of a ringed airfoil in which the example embodiments of the present disclosure may be utilized. The Mixer- Ejector Turbine includes tandem cambered shrouds, wherein each shroud is a substantially ringed airfoil, and a mixer/ejector pump. The primary shroud contains a rotor, which extracts power from a primary fluid stream. The tandem cambered shrouds and ejector provide for increased flow through the rotor allowing increased energy extraction due to higher flow rates compared to shroudless fluid turbines. The mixer/ejector pump transfers energy from the bypass flow to the rotor wake flow allowing higher energy per unit mass flow rate through the rotor. These two effects enhance the overall power production of the turbine system.

[0031] The term "rotor" is used herein to refer to any assembly in which one or more blades are attached to a shaft and able to rotate, allowing for the extraction of power or energy from wind rotating the blades. Example rotors include a propellerlike rotor or a rotor/stator assembly. Any type of rotor may be enclosed within the turbine shroud in the fluid turbine of the present disclosure.

[0032] The leading edge of a shroud may be considered the front of an airfoil, and the trailing edge of an airfoil may be considered the rear of the airfoil. A first component of the airfoil located closer to the front of the airfoil may be considered "upstream" of a second component located closer to the rear of the airfoil(i.e. the second component is "downstream" of the first component). Furthermore, the term "inner surface" is used herein to define a surface of ring airfoil that is inwardly facing towards a center axis of the airfoil. The term "outer surface" is used herein to define a surface that is outwardly facing away from the center axis of the airfoil such that the inner surface is closer to the center axis than the outer surface. Likewise, the term "suction side" or "low pressure side" of the ring airfoil is used herein to refer to the interior of the airfoil (i.e. radially inward of the inner surface) and the term "pressure side" of the airfoil is used herein to refer to exterior of the airfoil (i.e. radially outward from the outer surface).

[0033] The term "hoop strength" is used herein to refer to an ability of a structure to resist radially deformational forces about a circumference of a generally cylindrical or ring shaped structure and provide dimensional stability. For example, example embodiments of an airfoil described herein can include a rigid trailing edge region having a hoop strength to resist deformational forces of a fluid flow. [0034] In one embodiment, the present disclosure relates to a ring airfoil that includes a generally rigid structural leading edge region, an intermediate region formed of structurally rigid and non-rigid portions, and a generally rigid structural trailing edge region. The ring airfoil further comprises a flap on the trailing edge portion that is substantially perpendicular to the chord of the airfoil. An orientation of the flap with respect to the chord line can be fixed. In one embodiment, an exemplary embodiment of the ring airfoil can be implemented as a turbine shroud or a turbine mixer shroud that includes inward and outward turning segments that surround a rotor and/or an example embodiment of the ring airfoil can be implemented as an ejector shroud that generally surrounds an exit of a turbine shroud or a turbine mixer shroud.

[0035] Figure 1 is a front perspective view of an example ring airfoil 100. The airfoil 100 can have a body 102 extending circumferential about a center axis 105. The body 102 includes a leading edge region 112, an intermediate region 115 having one or more intermediate membrane portions 138 and one or more intermediate support portions 139, and a trailing edge region 116 having a flap 136. The leading edge region 112 can include a leading edge 162 of the airfoil 100 and the trailing edge region 116 can include a trailing edge 166 of the airfoil 100. The one or more intermediate portions 138 and 139 of the intermediate region 115 can extend between the leading edge region 112 and the trailing edge region 116 to mechanically couple the leading edge region 112 to the trailing edge portion 116. The one or more intermediate membrane portions 138 can be formed of one or more semi-rigid and/or non-rigid materials, e.g., as discussed herein, and the one or more intermediate support portions 139 can be formed of one or more a semi-rigid and/or rigid materials, e.g., as discussed herein. In an example embodiment, the ringed structurally rigid leading edge region combined with the rigid trailing edge region and intermediate discrete support portions provide sufficient rigidity to support the flap 136 on the trailing edge region 116 in a fixed relationship to a chord line and cambered line while implementing the intermediate membrane portion(s) to form surfaces of the intermediate region 115 of the airfoil 100. Thus, the structure of the airfoil 100 facilitates a fixed angular relationship between the flap 136 and the chord line 140 as well as between the flap 136 and the mean cambered line 170. Example embodiments of the airfoil 100 including a flap as described herein (e.g., flaps 136 and 236) can result in a ringed airfoil that exhibits similar performance characteristics as a conventional airfoils that have a greater chord length and no flap.

[0036] In an example embodiment, the one or more intermediate support portions 139 can provide structural support to the body 102 between the leading edge portion 112 and the trailing edge portion 116. The intermediate support portions 139 can be spaced apart from each other and can be distributed discretely and circumferentially about the center axis 105. The intermediate support portions 139 can be dimensioned and/or configured to specify a spatial relationship between the leading edge portion 112 and the trailing edge portion 116 and/or a shape of the one or more intermediate membrane portions 138. As one example, in one embodiment, the one or more intermediate support portions 139 can set a distance between the leading edge and the trailing edge of the airfoil 100, which corresponds to a chord line of the airfoil 100. As another example, in one embodiment, the intermediate support portions 139 can be contoured to taper away from the center axis 105 towards the trailing edge region 116 such that a diameter of the trailing edge portion is larger than a diameter of the leading edge portion 112. In some embodiments, the one or more intermediate membrane portions 138 can generally conform to the contours of the intermediate support portions 139. In some embodiments, the one or more intermediate portions 138 can be contoured independently of the one or more intermediate support portions.

[0037] In some embodiments, the leading edge region 112, the trailing edge region 116, and the one or more intermediate support portions 139 can be integrally formed as a single integral unit, and the one or more intermediate membrane portions 138 can be separately attached to form the body 102. In some embodiments, the leading edge region 112, the trailing edge region 116, the one or more intermediate portions 138, and the one or more intermediate support portions 139 can be separate components that are mechanically coupled together to form the body 102.

[0038] Some examples of plastic materials that can be used to form the leading edge region 112, the trailing edge region 116, and/or the one or more intermediate support portions 139 of the airfoil 100, or portions thereof, can include, but are not limited to polymers, such as a polyolefin or a polyamide, carbon composites, and/or metals. Some examples of polyolefins include polypropylene and polyethylene, such as high density polyethylene (HDPE) and low density polyethylene (LDPE). Some examples of polyamides include nylons. In some embodiments, polyvinyl chloride and plastisols can be used to form the leading edge region 112 and trailing edge region 116.

[0039] Some examples of materials that can be used to form the intermediate membrane portions 138 can include, but are not limited to fabrics, polymeric films, thin metal sheets, thin composites, marine shrink wrap, and the like. For embodiments in which fabric used, the fabric can be impregnated with a polymer resin (such as polyvinyl chloride) or a polymer film (such as modified polytetrafluoroethylene). Some examples of polymeric films include, but are not limited to polyvinyl chloride (PVC), polyurethane, polyfluoropolymers, multi-layer films of similar composition, and the like. Polyurethane films can be durable and can have good weatherability. Aliphatic versions of polyurethane films can be generally resistant to ultraviolet radiation. Some examples of polyfluoropolymers include polyvinyldidene fluoride (PVDF) and polyvinyl fluoride (PVF). Commercial versions are available under the trade names KYNAR® and TEDLAR®. Polyfluoropolymers generally have very low surface energy, which allow their surface to remain somewhat free of dirt and debris, and can shed ice more readily as compared to materials having a higher surface energy.

[0040] In example embodiments, the material or materials used to form the airfoil 100 and/or portions thereof can be reinforced with a reinforcing material, such as, for example, highly crystalline polyethylene fibers, paramid fibers, and polyaramides.

[0041] The leading edge region 112, the trailing edge region 116, the one or more intermediate support portions 138, and/or the one or more intermediate membrane portions 139 can be formed of multiple layers of material, for example, comprising two, three, or more layers. Multi-layer constructions may add strength, water resistance, ultraviolet (UV) stability, and other functionality.

[0042] In some embodiments, the leading edge region 112 of the airfoil can be a sandwich composite material, such as an epoxy-impregnated e-glass matte, and the space inside the sandwich composite can be filled with foam. This configuration provides for high beam stiffness construction with overall low density.

[0043] Figure 2 is a cross sectional view of an example embodiment of a ring airfoil of the present disclosure along the line 2-2 of Figure 1 depicting one of the intermediate membrane portions 138 of the airfoil 100. The leading edge region 112 can extend from the leading edge 162 to the intermediate region 115. The leading edge region 112 can have a volumetric form with varying thickness TL between the inner surface 132 (i.e. suction side surface 132) and the outer surface 134 (i.e. pressure side surface 134), thus creating a volume of varying thickness TL- The leading edge 162 of the airfoil 100 can be generally rounded, bull-nosed, or otherwise shaped to form an aerodynamic surface for dividing a fluid into at least two flows or streams (e.g., a suction side along the inner surface 132 and a pressure side along the outer surface 134. The cross-sectional shape of the leading edge region 112 can taper away from the leading edge 162 increasing in cross-sectional thickness TL and then can taper towards a center or mean camber line 170 decreasing in cross-sectional thickness TL to a joint 131 between the intermediate membrane portion 138 along the mean camber line 170 such that the cross-sectional thickness TL of the leading edge region 112 generally varies from the leading edge 162 to joint 131 mechanically coupling the leading edge region 112 to the intermediate membrane portions 138. The center or mean camber line 170 is generally positioned midway between outer and inner surfaces 132 and 134 of the airfoil 100, respectively, along the longitudinal extent of the airfoil 100.

[0044] As depicted in Figure 2, a chord 140 defines a length of the airfoil 100 between the leading edge 162 and the trailing edge 166 of the airfoil 100, which can be determined based on the mean camber line 170. A cross-sectional thickness of the airfoil 100 can correspond to a distance from the outer surface 134 to the inner surface 132 of the airfoil 100, measured perpendicular to the mean camber line 170, and can vary with distance along the mean camber line 170 such that the cross-sectional thickness of the airfoil 100 varies over a length of the airfoil 100 from the leading edge 162 to the trailing edge 166. An interior area (or volume) 113 formed by the surfaces 132, 134 in the leading edge region 112 can be hollow, or can be filled with support members for providing structural rigidity and shape. In accordance with one embodiment, a foam material 172 may be utilized in providing both shape and structural rigidity to the assembly.

[0045] In some embodiments, the one or more intermediate membrane portions 138 of the intermediate region 115 can extend linearly from the leading edge region 112 to the trailing edge region 116. In some embodiments, the intermediate membrane portions 138 can have a curvature between the leading edge region 112 and the trailing edge region 116. The intermediate membrane portions 138 can have a substantially uniform and constant cross-sectional thickness ¾ along its length. In the example embodiment, the surfaces 132, 134 can be positioned adjacent to each other and can be in contact to form the intermediate membrane portions 138 such that the cross-sectional thickness ¾ of the intermediate membrane portions 138 can be approximately equal the thickness of the material or materials between the surfaces 132, 134. In some embodiments, the intermediate membrane portions 138 can be formed of a sheet of material with a thickness such that no space or void exists in the intermediate membrane portions 138. For example, the intermediate membrane portions 138 can be a curved planar form with relatively constant thickness.

[0046] In one example embodiment, the intermediate membrane portions 138 can be tacked, adhered, friction fit, or otherwise attached or fixed to the leading edge region 112 to secure the intermediate membrane portions 138 to the leading edge region 112. In one example embodiment, the joint 131 between the leading edge region 112 and the intermediate membrane portions 138 can be formed by a groove or channel 117 configured to receive and hold an upstream end 143 of the intermediate membrane portions 138. For example, the upstream end 143 can have a circular cross section corresponding to a circular cross section of the channel 117 such that the upstream end 143 of the intermediate membrane region 138 can slide into, engage, and be retained by the channel 117 of the leading edge region 112.

[0047] In example embodiments, the trailing edge region 116 can be formed as a ringed structure extending circumferentially about the center axis 105 and the trailing edge 116 can have a diameter or width that is greater than a diameter or width of the leading edge 162. An end of the trailing edge region 116 opposite of the trailing edge 166 can include a recessed portion, such as a notch or channel 182 configured to receive and mechanically couple to the intermediate membrane portions 138. In an example embodiment, the trailing edge region can provide rigidity to the trailing edge 166 of the airfoil 100 such that the trailing edge 166.

[0048] The trailing edge region 116 can include the flap 136 extending therefrom. In one example embodiment, the flap 136 can extend radially outward from or proximate to the trailing edge 166. The flap 136 can have a length L that extends at an angle Θ with respect to the chord line 140. In an example embodiment, the angle Θ between the chord line 140 and the flap 136 can be fixed. The length L of the flap 136 can be about ten to about thirty percent less than a length of the chord line 140. In an example embodiment, the length L of the flap 136 can extend perpendicularly to the chord line 140 and can be implemented to turn the airflow along the outer surface 134. In example embodiments, the flap 136 can include perforations 184 to allow some air to flow through the flap 136 to reduce the force exerted on the flap by the airflow. In exemplary embodiments, the flap 136 can be formed of the same or a similar material as the intermediate membrane portions 138.

[0049] Figure 3 is a cross sectional view of the airfoil of Figure 1 along the line 3-3 of Figure 1 depicting one of the intermediate support portions 139 of the intermediate region 115, which can be disposed between and between the leading edge region 112 and the trailing edge region 116. In one example embodiment, as depicted in Figure 3, the intermediate support portions 139 can be integrally formed with the leading edge region 112 such that the intermediate support portions 139 forms a unitary structure with the leading edge region 112 and the intermediate support portions 139 can be mechanically coupled to the trailing edge region 116. In another example embodiment, the intermediate support portions 139 can be mechanically coupled to the leading edge region 112 and/or the trailing edge region 116. In yet another example embodiment, the intermediate support portions 139 can be integrally formed with the leading edge region 112 and/or the trailing edge region 116.

[0050] The intermediate support portions 139 can provide structural support for the air foil 100 to define a distance between the leading edge region 112 and the trailing edge region 116 and/or can provide a support structure for the intermediate membrane portions 139, e.g., to define a contour of the intermediate membrane portions 138. The intermediate rigid portions 139 can be elongate members have a generally rod- like or bar-like configuration. The intermediate support portions 139 can be configured to engage the channel 182 formed in the trailing edge region 116 to mechanically couple the intermediate support portions 139 to the trailing edge region 116. In some embodiments the intermediate support portions can be integrally formed with the leading edge region 112 and/or the trailing edge region 116.

[0051] In some embodiments, the intermediate support portions 139 can extend linearly from the leading edge region 112 to the trailing edge region 116. In some embodiments, the intermediate support portions 139 can have a curvature between the leading edge region 112 and the trailing edge region 116. The intermediate support portions 139 can have a substantially uniform and constant cross-sectional thickness Tis along the length. In the example embodiment, the surfaces 132, 134 of the intermediate support portions 139 can be positioned adjacent to each other and can be in contact to form the intermediate support portions 139 such that the cross-sectional thickness ¾ of the intermediate support portions 139 can be approximately equal the thickness of the material or materials between the surfaces 132, 134. In some embodiments, the intermediate support portions 139 can be formed of a sheet of material with a thickness such that no space or void exists in the intermediate support portions 139. For example, the intermediate support portions 139 can be a curved planar form with relatively constant thickness.

[0052] In one embodiment, the intermediate membrane portions 138 can encompass or encircle the intermediate support portions 139. In some embodiments, the intermediate membrane portions 138 can be tacked, adhered, friction fit, or otherwise attached or fixed to the intermediate support portions 139 to secure the intermediate membrane portions 138 to the intermediate support portions 139. For example, in one embodiment, a polyethylene shrink wrap can be used as the intermediate membrane portion(s) 138, and the polyethylene shrink wrap can encircle the intermediate support portions 139 and heat can be applied to the polyethylene shrink wrap to shrink the polyethylene shrink wrap onto the intermediate support portions 139 forming a tight friction fit. In some embodiments, the intermediate membrane portions 138 can each extend between a pair of intermediate support portions 139 from the leading edge region 112 to the trailing edge region 116.

[0053] Referring to Figure 4, an orthographic detail section view of trailing edge region 116 of the airfoil 100 of Figure 2 is depicted. The example embodiment includes the flap 136 on the trailing edge 116. The flap 136 is generally perpendicular, or in other words, is at the angle Θ between approximately 85° and 120° relative to the chord line 140 of the airfoil cross section. In some embodiments the trailing edge region 116 can include a rigid member 148 that engages the membrane intermediate portion 138 (e.g., via channel 182). The rigid member 148 is engaged with a ring 146 that is in turn engaged with a flap 136. The ring 146 provides hoop strength to the rigid member 148. The flap 136 contains at least one ring 144 that provides hoop strength to the outer edge of the flap 136. As discussed above, rigid structural support members in the form of the intermediate support portions 139 are spaced radially about the ringed airfoil proximal to intermediate membrane portions 138 (Figures 1 and 3). The intermediate support portions 139 provide structure to support the location and configuration of the trailing edge 116. The structural support provided by the intermediate support portions 139 maintains the angle Θ of the flap 136 with respect to the chord 140 and provides a structure to support the membrane intermediate portions 138.

[0054] Referring to Figure 5, an orthographic cross section of a ring airfoil of an example embodiment 100 is depicted. The direction and path of fluid flow around the airfoil 100, from the leading edge 112 to the trailing edge 116 is represented by arrow 152 on the suction side 132 (i.e. the inner surface 132), and arrow 154 on the pressure side 134 (i.e. the outer surface).

[0055] Referring again to Figure 5, the flap 136 causes an area of stagnation 141 in the flow on the pressure side of the airfoil 134. The addition of the flap 136 on or proximate to the trailing edge 166 of the airfoil 100 also generates vortices 118 downwind of the trailing edge 116 of the airfoil 100. The addition of the flap 136 causes the air stream 154 on the pressure side 134 of the airfoil 100 to be pushed upward thus allowing the fluid stream 152 on the suction side 132 of the airfoil 100 to stay attached to the surface and generate improved circulation of the fluid streams.

[0056] Figure 6 depicts a perspective view of another example airfoil 200. A body 202 of the airfoil 200 can include a leading edge region 212, an intermediate region 215, and a trailing edge region 216. The airfoil 200 can include mixing elements 226, 228 that may be formed by the intermediate region 215 and the trailing edge region 216. As depicted, the mixing lobes may include low energy mixing lobes 228 that extend inward toward the central axis 205, and high energy mixing lobes 226 that extend outward away from the central axis 105. In other words, the trailing edge 124 of the turbine shroud 104 is shaped to form two different sets of mixing lobes. The mixing lobes 126, 128 can form a general circular crenellated or circumferential undulating in-and-out shape about the center axis 205.

[0057] The trailing edge region 216 of the airfoil 200 can be formed of a rigid material and can have a general circular crenellated or circumferential undulating in- and-out shape about the center axis 205, which can import the structural configuration of the mixing lobes 126, 128 to intermediate membrane portions 238 of the intermediate region 215. The trailing edge region can include one or more flaps 236. In an example embodiment, as depicted in Figure 6, each low energy mixing lobe 228 can include one of the flaps 236 and high energy mixing lobes 226 can be devoid of the flap 236. In another example embodiment, the high energy and low energy mixing lobes 226, 228 can include a flap 236. In yet another example embodiment, the flap 236 can extend continuously along the trailing edge region 216 to form a single flap continuously disposed about the center axis 205. In an example embodiment, the ringed structural leading edge region 212 combined with the rigid trailing edge region 216 and intermediate discrete support portions of the intermediate region 215 provide sufficient rigidity to support the flap 136 on the trailing edge region 116 in a fixed relationship to the chord line while implementing the intermediate membrane portion(s) as to form the surfaces of the intermediate region of the airfoil. Thus, the structure of the airfoil 100 facilitates provide a fixed angular relationship between the flap 136 and the chord line 140 as well as between the flap 136 and the mean cambered line 170. Example embodiments of the airfoil 200 including the flap 236 can result in a ringed airfoil that exhibits similar performance characteristics as a conventional airfoils that have a greater chord length and no flap.

[0058] In an example embodiment, the one or more intermediate support portions 239 can provide structural support to the body 202 between the leading edge portion 212 and the trailing edge portion 216. The intermediate support portions 239 can be spaced apart from each other and can be distributed discretely and circumferentially about the center axis 205. The intermediate support portions 239 can be dimensioned and/or configured to specify a spatial relationship between the leading edge portion 212 and the trailing edge portion 216. As one example, in one embodiment, the one or more intermediate support portions 239 can set a distance between the leading edge and the trailing edge of the airfoil 200, which corresponds to a chord line of the airfoil 200.

[0059] Figure 7 is a cross sectional view of the airfoil 200 of Figure 6 along the line 7-7. As depicted in Figure 7, the cross section of the airfoil 200 generally corresponds to the cross-section of the airfoil 100 in that that the leading edge region includes a varying volume and the intermediate membrane portion(s) 238 includes a generally uniform volume. The leading edge 262 of the airfoil 100 can be generally rounded, bull-nosed, or otherwise shaped to form an aerodynamic surface for dividing a fluid into at least two flows or streams (e.g., a suction side along the inner surface 232 and a pressure side along the outer surface 234. The cross-sectional shape of the leading edge region 212 can taper away from the leading edge 262 increasing in cross-sectional thickness and then can taper towards a center or mean camber line 270 decreasing in cross-sectional thickness to the intermediate region along the mean camber line 270. The center or mean camber line 270 is generally positioned midway between outer and inner surfaces 232 and 234 of the airfoil 200, respectively, along the longitudinal extent of the airfoil 200.

[0060] As depicted in Figure 7, a chord 240 defines a length of the airfoil 200 between the leading edge 262 and the trailing edge 266 of the airfoil 200, which can be determined based on the mean camber line 270. The intermediate membrane portion 238 can have a substantially uniform and constant cross-sectional thickness along its length. In the example embodiment, the surfaces 232, 234 can be positioned adjacent to each other and can be in contact to form the intermediate membrane portion 238.

[0061] Similar to the intermediate region 115 of the example airfoil 100 described herein, the intermediate region 215 can include intermediate membrane portions 238 and intermediate support portions 239. The intermediate membrane portions 238 can be formed of semi-rigid and/or non-rigid materials and the intermediate support portions 239 can be formed of semi-rigid and/or rigid materials. The intermediate region 215 provides the transitional area between the inward turning mixing elements 226 and the outward turning mixing elements 228. The rigid trailing edge region 216 provides the structure to support the membrane surfaces that make up the mixing elements 226 and 228. In example embodiments, the trailing edge region 216 can be formed as a rigid structure extending about the center axis 205 in the circumferential undulating manner. In an example embodiment, the trailing edge region 216 can provide rigidity to the trailing edge 266 of the airfoil 200 such that the trailing edge 266.

[0062] The trailing edge region 216 can include the flap 236 extending therefrom. In one example embodiment, the flap 236 can extend radially outward from or proximate to the trailing edge 266. The flap 236 can have a length L that extends at an angle θ' with respect to the chord line 240. In an example embodiment, the angle θ' between the chord line 140 and the flap 236 can be fixed and/or the length L of the flap 236 can be about ten to about thirty percent less than a length of the chord line 240. In an example embodiment, the length L of the flap 236 can extend perpendicularly to the chord line 240 and can be implemented to turn the airflow along the outer surface 234. In the present example embodiment, the flap 236 is engaged with the trailing edge 266 of the outward turning mixing elements 228. The trailing edge 266 is comprised of similar components as depicted and described in Figures 3-4 . In example embodiments, the flap 236 can include perforations 284 to allow some air to flow through the flap 236 to reduce the force exerted on the flap 236 by the airflow. The flap 236 is dimensioned and configured to allow a fluid flow flowing along the inner surface to remain attached to the inner surface.

[0063] Figure 8 depicts a front perspective view of an example shrouded fluid turbine 300 in the form of a wind turbine having a support structure 302, an energy extracting assembly 345 and a turbine shroud formed by the example airfoil 100 having the leading edge region 112, the intermediate region 115, and the trailing edge region 116. The energy extracting assembly 345 can include a nacelle body 350 and a rotor 340. The rotor 340 is engaged with the nacelle body 350 at the proximal end of the rotor blades. The airfoil 100 can encircle the rotor 340. In one example, embodiment the leading edge 166 of the airfoil 100 can be positioned up stream of the rotor 340 and/or the trailing edge 166 of the airfoil 100 can be positioned downstream of the rotor 340. The leading edge 162 can form an inlet of the shrouded fluid turbine 300 and the trailing edge 166 can form the exhaust of the shrouded fluid turbine 300. The flap 136 can allow a fluid flow (e.g., airflow) flowing along the inner surface of the air foil to remain attached to the inner surface. In an example embodiment, the airfoil 100 can be positioned relative to the nacelle body 350 and rotor 340 using elongate support structures 307 such that the nacelle body 350, the rotor 340, and the airfoil 100 are position coaxially with respect to each other about the center axis 105.

[0064] Figure 9 depicts a front perspective view of an example shrouded fluid turbine 400 in the form of a wind turbine having the support structure 302, the energy extracting assembly 345, and a turbine mixer shroud formed by the example airfoil 200 having the leading edge region 212, the intermediate region 215, and the trailing edge region 216. The airfoil 200 can encircle the rotor 340. In one example, embodiment the leading edge 266 of the airfoil 200 can be positioned up stream of the rotor 340 and/or the trailing edge 266 of the airfoil 200 can be positioned downstream of the rotor 340. The leading edge 262 can form an inlet of the shrouded fluid turbine 400 and the trailing edge 266 can form the exhaust of the shrouded fluid turbine 400. As described above, the trailing edge 266 includes inward turning mixing elements 226 and outward turning mixing elements 228. The inward turning mixing elements 226 curve inward toward the central axis 205 and the outward turning mixing elements 228 curve outward from the central axis 205. The flap 236 can allow a fluid flow (e.g., airflow) flowing along the inner surface of the air foil to remain attached to the inner surface. In an example embodiment, the airfoil 200 can be positioned relative to the nacelle body 350 and rotor 340 using elongate support structures 307 such that the nacelle body 350, the rotor 340, and the airfoil 200 are position coaxially with respect to each other about the center axis 205.

[0065] Figure 10 is a front, perspective view of an example embodiment of a shrouded fluid turbine 500 incorporating example embodiments of the ring airfoils 100 and 200 of the present disclosure. Figure 11 is a rear, perspective view of the shrouded fluid turbine of Figure 10. Figure 12 is a side perspective, detail, section view of the shrouded fluid turbine 500 of Figures 10 and 11 cut through the outward turning mixing elements 228. Figure 13 is a side perspective, detail, section view of the shrouded fluid turbine 500 of Figures 10 and 11 cut through the inward turning mixing elements 226. The detail cross sections of Figure 12 and 13 depict the ring airfoils 100 and 200 of the present disclosure incorporated into the mixer-ejector turbine shrouds. The ring airfoil 100 includes the leading edge region 112, the intermediate region 115, and the trailing edge region 116. The ring airfoil 200 includes the leading edge region 212, the intermediate region 215, and the trailing edge region 216.

[0066] In an example, embodiment, the shrouded fluid turbine 500 may be referred to as a mixer/ejector fluid turbine, where the airfoils 200 and airfoil 100 form an mixer/ejector pump. Referring to Figures 10-13, the shrouded fluid turbine 500 is supported by the support structure 302 and comprises a turbine mixer shroud formed by an example embodiment of the airfoil 200, the energy extract assembly formed by the nacelle body 350 and the rotor 340, and an ejector shroud formed by the airfoil 200. The rotor 340, airfoil 200 (i.e. turbine mixer shroud), and the airfoil 100 (i.e. the ejector shroud) are coaxial with each other, i.e. they share a common central axis 505. In an example embodiment, the airfoil 200 can be positioned relative to the nacelle body 350 and rotor 340 using elongate support structures 307 and the airfoil 100 can be positioned relative to the airfoil 200 using elongate support structures 506.

[0067] In one example, embodiment the leading edge 266 of the airfoil 200 can be positioned up stream of the rotor 340, the trailing edge 266 of the airfoil 200 can be positioned downstream of the rotor 340, the leading edge 162 of the airfoil 100 can be disposed downstream of the rotor 340, and/or the trailing edge 166 of the air foil 166 can be positioned downstream of the trailing edge 266. The leading edge 262 can form an inlet of the airfoil 200 in the shrouded fluid turbine 400 and the trailing edge 266 can form the exhaust of the airfoil 200 in the shrouded fluid turbine 400.

[0068] The ejector shroud formed by the airfoil 100 includes a front end or inlet end defined by the leading edge 162, and a rear end or exhaust end defined by the trailing edge 166.

[0069] Figure 14 depicts the trailing edge regions 116 and 216 in more detail to illustrate example perforation 184 and 284, respectively. The perforations 184 and 284 can be formed in the flaps 136 and 236, respectively to allow some air to flow through the flaps 136, 236 to reduce the force exerted on the flap 236 by the airflow.

[0070] Figure 15 is a front, perspective view of another exemplary embodiment of a shrouded fluid turbine 600 incorporating example ring airfoils 700 and 800 of the present disclosure. Figure 16 is a side, orthographic, detail, section view of the fluid turbine of Figure 15. Referring to Figures 15-16, the shrouded fluid turbine 600 is supported by the support structure 302 and includes the energy extracting assembly 345 having the rotor 340 and the nacelle body 350. The ring airfoil 700 forms a turbine shroud and the ring airfoil 800 forms an ejector shroud of the shrouded fluid turbine 600. The rotor 340, turbine shroud (i.e. the airfoil 700), and ejector shroud (i.e. the airfoil 800) are coaxial with each other, i.e. they share a common central axis 605.

[0071] The airfoils 700 and 800 can be formed in a similar manner to the example airfoils 100 and 200, as described herein. The airfoil 700 can include a leading edge region 712 having a leading edge 762 that forms a front end or inlet end of the airfoil 700. The leading edge region 712 can have a substantially similar or identical cross- sectional structure (depicted in Figure 16) to that of the leading edge regions 112 and 212, as described herein. [0072] The airfoil 700 also includes a trailing edge regions 716 having a trailing edge 766 that form a rear end or outlet (exhaust) end of the airfoil 700. The trailing edge region 716 can have a substantially similar or identical cross-sectional structure (depicted in Figure 16) to that of the trailing edge region 112, as described herein. In the present example, the trailing edge region 716 can have multi-sided polygon shape having a faceted structure. For example, the trailing edge regions 716 can include facets 775 that are enjoined at nodes 777.

[0073] The airfoil 800 includes a leading edge region 812 having a leading edge 862 that forms a front end or inlet end of the airfoil 800 and a rear end. The airfoil 800 also includes a trailing edge region 816 having a trailing edge 866 that forms an exhaust end or outlet end of the airfoil 800. The airfoil 800 includes a faceted annular airfoil for which the leading edge region 812 can have a substantially similar or identical cross section as the leading edge regions 112, 212, and 712 described herein. In the present example, the trailing edge region 816 can have multi-sided polygon shape having a faceted structure. For example, the trailing edge regions 816 can include facets 875 that are enjoined at nodes 877.

[0074] The airfoils 700 and 800 can include intermediate regions 715 and 815, respectively, that extend between the leading edge regions 712 and 812, respectively, to the trailing edge regions 716 and 816, respectively. The intermediate regions 715 and 815 can be formed of intermediate support portions and intermediate membrane portions.

[0075] A detail cross section of the shrouded turbine of Figure 15 is depicted in Figure 16 and illustrates the faceted annular airfoils 700 and 800 incorporated into the mixer-ejector turbine shrouds. The airfoils 700 and 800 have the voluminous leading edge regions 712 and 812, respectively, that is engaged with the intermediate regions 715 and 815, respectively, which form a transitional area between the leading edge regions 712/812 and the trailing edge regions 716/816, respectively. A rigid trailing edge region 716 is comprised of similar components as shown and described herein and provides the structure to support the intermediate membrane portions of the intermediate region 715.

[0076] In some embodiments, intermediate support portions may be incorporated into either or both, nodes 777 or facets 775, which are generally formed the intimidate membrane portions. A flap 736 is engaged with the trailing edge region 716 of the airfoil 700 to extend from the trailing edge at a fixed angle (e.g., perpendicular) with respect to the chord line of the air foil 700. Likewise, the airfoil 800 is comprised of the voluminous leading edge region 812, the intermediate region 815, and the trailing edge region 816. A flap 836 is engaged with the trailing edge region 816 of the airfoil 800 to extend from the trailing edge at a fixed angle (e.g., perpendicular) with respect to the chord line of the air foil 800. The intermediate region 815 can include intermediate membrane portions depicted as the facets 875 and nodes 877. Intermediate support portions 839 of the intermediate region 815 can be dispersed radially about the central axis 705 and also engage with the airfoil 700 to connect the airfoil 700 to the airfoil 800.

[0077] Figures 17 depicts a front perspective view of an example shrouded fluid turbine 900 in the form of a wind turbine having the support structure 302, the energy extracting assembly 345 and a turbine shroud formed by the example airfoil 700 having the leading edge region 712, the intermediate region 715, and the trailing edge region 716. The energy extracting assembly 345 can include a nacelle body 350 and a rotor 340. The rotor 340 is engaged with the nacelle body 350 at the proximal end of the rotor blades. The airfoil 700 can encircle the rotor 340. In one example, embodiment the leading edge 766 of the airfoil 700 can be positioned up stream of the rotor 340 and/or the trailing edge 766 of the airfoil 700 can be positioned downstream of the rotor 340. The leading edge 762 can form an inlet of the shrouded fluid turbine 900 and the trailing edge 766 can form the exhaust of the shrouded fluid turbine 900. The flap 736 can allow a fluid flow (e.g., airflow) flowing along the inner surface of the air foil to remain attached to the inner surface. In an example embodiment, the airfoil 700 can be positioned relative to the nacelle body 350 and rotor 340 using elongate support structures 307 such that the nacelle body 350, the rotor 340, and the airfoil 100 are position coaxially with respect to each other about the center axis 605.

[0078] Example embodiments of the present disclosure advantageously provide a ringed airfoil having a generally lightweight structure relative to conventional ringed airfoils. Example embodiments of the airfoil including the flap can result in a ringed airfoil that exhibits similar performance characteristics as a conventional airfoil with a greater chord length and no flap. Furthermore, example embodiments of the present disclosure provide for generally easier and less time consuming maintenance and repair of the airfoils as compared to conventional airfoils, particularly with respect to the maintenance and repair of the intermediate membrane portions and the flap.

[0079] As set forth previously, the present embodiment is not specific to an ejector of a MET and may be applied to those ducted or shrouded fluid turbines as understood in the art. The present disclosure has been described with reference to example embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS We claim

1. An aerodynamically contoured ring airfoil comprising; a body extending circumferentially about a center axis having an aerodynamic structure formed by an outer surface and an inner surface, the outer and inner surfaces extend axially with respect to the center axis along a camber line, the body including a leading edge region, a trailing edge region, and an intermediate region extends between the leading edge region and the trailing edge region; the leading edge region having a non-uniform cross-sectional thickness extending along the camber line defined by the outer surface and the inner surface of the body; and the trailing edge region including a flap extending therefrom and orientated at an angle with respect to a chord line of the body to allow a fluid flow flowing along the inner surface to remain attached to the inner surface.

2. The airfoil of claim 1, wherein the flap extends from the trailing edge region perpendicularly to the chord line.

3. The airfoil of claim 1, wherein the length of the flap is about one-tenth to about one-third a length of the chord line.

4. The airfoil of claim 1, wherein the flap includes at least one perforation to permit fluid flow through the flap.

5. The airfoil of claim 1, wherein the flap extends from a trailing edge of the airfoil.

6. The airfoil of claim 1, wherein the flap extends between a first ring structure and a second ring structure, the first and second ring structures providing a hoop strength to the flap.

7. The airfoil of claim 6, wherein the first ring structure provides a hoop strength to the trailing edge region of the body.

8. The airfoil of claim 1, wherein the intermediate region comprises at least one intermediate support portion extending between the leading edge region and the trailing edge region.

9. The airfoil of claim 8, wherein the intermediate support portion is composed of a rigid material.

10. The airfoil of claim 8, wherein the intermediate support portion has a uniform cross-sectional thickness extending along the mean camber line defined by the outer surface and the inner surface of the body.

11. The airfoil of claim 8, wherein the intermediate region comprises at least one intermediate membrane portion extending between the leading edge region and the trailing edge region.

12. The airfoil of claim 11, wherein the intermediate membrane portion has a uniform cross-sectional thickness extending along the mean camber line defined by the outer surface and the inner surface of the body.

13. The airfoil of claim 11, wherein the intermediate region is composed of a non- rigid material.

14. The airfoil of claim 11, wherein the intermediate support portions provides structural support to the intermediate membrane portion.

15. An energy extracting shrouded fluid turbine comprising: an energy extracting assembly including a rotor disposed radially about a center axis; and an airfoil having a body extending circumferentially about the center axis, the body having an aerodynamic structure formed by an outer surface and an inner surface, the outer and inner surfaces extend axially with respect to the center axis along a camber line, the body including a leading edge region, a trailing edge region, and an intermediate region extends between the leading edge region and the trailing edge region; the leading edge region having a non-uniform cross-sectional thickness extending along the camber line defined by the outer surface and the inner surface of the body; and the trailing edge region including a flap extending therefrom and orientated at an angle with respect to a chord line of the body to allow a fluid flow flowing along the inner surface to remain attached to the inner surface.

16. The fluid turbine of claim 15, wherein the flap extends from the trailing edge region perpendicularly to the chord line.

17. The fluid turbine of claim 15, wherein the length of the flap is about one-tenth to about one-third a length of the chord line.

18. The fluid turbine of claim 16, wherein the flap includes at least one perforation to permit fluid flow through the flap.

19. The fluid turbine of claim 15, wherein the flap extends from the trailing edge region of the airfoil, the flap extending between a first ring structure and a second ring structure, the first and second ring structures providing a hoop strength to the flap and the first ring structure providing a hoop strength to the trailing edge region of the body.

20. The fluid turbine of claim 15, wherein the intermediate region including at least one intermediate support portion composed of a rigid material and at least one intermediate membrane portion composed of a non-rigid material, the intermediate support portion and the intermediate membrane portion extending between the leading edge region and the trailing edge region.

21. The fluid turbine of claim 20, wherein at least one of the intermediate support portion or the intermediate membrane portion has a uniform cross-sectional thickness extending along the mean camber line defined by the outer surface and the inner surface of the body.